Previous investigations have demonstraated that hypothalamic and ovarian mechanisms control Adenohypophysial Luteinizing Hormone (LH) secretion, y et their role in the control of Follicle Stimulating Hormone (FSH) secretion is much less known. Therefore, various factors controlling the pituitary release of FSH during the periovulatoary period, with particular emphasis on the second phase of FSH release will be examined. Specific hypothalamic nuclei/areas will be ablated (electrolytic lesions) and/or electrically stimulated before the proestrous phase to determine which of these specific areas may regulate pituitary release of FSH. In a second series of experiments, exogenous Gonadotropin Release Hormone (GnRH) will be administered in a pulasatile pattern to cause FSH secretion which accurately simulates the normal physiologic pattern. Another series of experiments is proposed to determine more specifically the roles of ovarian inhibin and testosterone on the pituitary release of FSH. They will be administered either alone or in combination prior to either the first phase of FSH release or the second phase of FSH release. Inhibin will also be administered intravenously or into specific hypothalamic nuclei to determine whether it acts at the level of the hypothalamus.